It is well known to provide glazing systems for curtain walls, storefront framing systems, and the like wherein the glazing system comprises a frame member and a cooperating pressure plate for retaining glazing panels in place against the frame member. A typical prior art glazing system of this type comprises an extruded aluminum pressure plate fastened to the outer face of the frame member by screws. A pair of gaskets is mounted to the pressure plate within raceways formed on the outer edges of the pressure plate. In turn the gaskets bear against marginal portions of the outer surface of the glazing panel. Where it is desired to provide a thermally insulated glazing system, a thermal separator is interposed between the aluminum pressure plate and the associated frame member.
This type of glazing system suffers a disadvantage in that it is labor-intensive to install. Four separate components--the pressure plate, two gaskets, and the thermal separator--must be installed to each frame member. In addition, the multiplicity of parts requires greater inventory and increases the likelihood of improper installation by inexperienced or unskilled workers. Thus there is a need for a thermally insulated glazing system which reduces the number of parts which must be installed.
A further difficulty inherent in prior art pressure plate designs arises from the fact that the gaskets are often stretched during installation onto the pressure plate. Over time the gaskets tend to return to their original state and thus shrink relative to the pressure plate. This shrinkage can compromise the integrity of the weatherproofing and permit water to penetrate the joint. Thus there is a need for a thermally insulated glazing system which eliminates relative movement between the gaskets and the pressure plate.